It is generally known to blend thermoplastic polymers with particulate material to impart specific properties to composites made therefrom. For example, particulate material is blended with thermoplastic polymers to create composites having improved puncture resistance, strength, tear resistance, electrical conductivity, and other characteristics. Specifically, it is known to blend clays, fibers or other like particulate material into a thermoplastic polymer and to mix the blend while the thermoplastic is in a molten state to form a composite material having increased strength when solidified and molded into articles.
Moreover, it is known to blend high specific gravity materials into thermoplastic polymers to attempt to approximate or mimic the characteristics of high specific gravity metals, such as lead. Specifically, it is desirable to create a composite material having the properties of lead, such as, for example, malleability and high specific gravity.
Malleable materials may be utilized in a number of applications. Specifically, high specific gravity malleable materials may be utilized in ammunition cores or fishing weights. For example, ammunition cores and fishing weights are typically made from lead. In the case of ammunition cores, lead is desirable because it has the dual property of high specific gravity and malleability, such that it is useful as a projectile and can easily be formed into ammunition cores by swaging the lead without distortion of the jacket or casing.
However, it is known that lead causes developmental problems in humans, particularly children, and animals, such as birds (particularly the common loon), fish, and other animals, and can have acute effects on individuals when exposed thereto at high concentrations. In many places around the world, lead has caused environmental contamination due to its wide use in ammunition, fishing weights, and other products. For example, firing ranges, where lead-based projectiles are fired from firearms, can be seriously contaminated with spent lead cores that litter target sites. Clean-up of lead contaminated sites is a major priority of the U.S. Government. The armed forces have allocated millions of dollars to clean sites polluted with lead from firearms. Therefore, a suitable replacement for lead is desired and sought.
However, typical high specific gravity thermoplastic composite materials do not have the proper properties to make them useful as lead substitutes because they lack such a property as malleability. In addition, many non-lead, high specific gravity thermoplastic and metal-containing composite materials may not be malleable like lead, in that the materials do not deform and retain their shapes properly to be useful, such as, for example, in projectiles or fishing weights.
For example, when swaging a bullet in an ammunition jacket or casing with a high specific gravity material, distortion can occur in the ammunition jacket or casing due to unyielding properties of the high specific gravity material. Therefore, the high specific gravity material must have the dual properties of having a high specific gravity while also being malleable such that the material deforms and substantially retains its shape after deformation when encased by an ammunition jacket or casing. This allows the ammunition to be properly fired from a firearm without damaging the firearm or having an unintended trajectory. Moreover, high specific gravity malleable materials should be deformable in molds to form precise and repeatable items, such as fishing weights and the like.
Prior attempts to create composite materials having high specific gravity and malleability have included melt-mixing a thermoplastic material with a high specific gravity particulate filler. However, these high specific gravity composite materials do not provide adequate lead-like characteristics, in that the materials do not have both high specific gravities while also having the ability to deform and hold their shapes properly.
Therefore, a need exists for a malleable composite material made from thermoplastic polymers or blends thereof and particulate material. Specifically, a need exists for a thermoplastic composite material having particulate filler and malleability, such that the thermoplastic composite material can readily deform under pressure without any or significant recovery of its shape. Moreover, a need exists for a thermoplastic composite material having the dual characteristics of high specific gravity and malleability such that the material may be useful as a substitute for lead or lead-based materials, but without the toxic characteristics of lead or lead-based materials. Moreover, a need exists for a malleable thermoplastic composite material that may be easily extruded to form pellets or molded articles. In addition, a need exists for a high specific gravity thermoplastic composite material that may be utilized in the manufacture of products as a lead replacement, such as, for example, in projectiles and fishing weights.